Electric resistance device



Feb. '10; 1925 1,525,838

, A. E. WALLER ELECTRIC RESISTANCE DEVICE Filed March 14, 1921 Patented Feb. 10, 1925.

UNITED stares ALFRED ERNEST WALLEB, OF B RONXVILLE, NEW YORK, ASSIGNOR TO WARD PATENT OFFICE.

' LEONARD ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

" ELECTRIC RESISTANCE DEVICE.

5 .1 Application filed larch 14, 1921. Serial No. 452,186.

To all whom it may concern:

Be it known that I, ALFRED E. IVALLER, a citizen of the United States, residing at Bronxville, in the county of Westchester and State of New York, have invented certain new and useful Improvements in Electric Resistance Devices, of which the following is a specification. I

This invention relates to electric resistance devices and to resistance conductors and more particularly to resistance devices or resistance units wherein the resistive conductor is mounted upon an insulating support and insulated and protected by an adhesive coating of insulating material, such as vitreous enamel. It also relates to an improved method of making and forming a resistance conductor, whereby any desired resistance per unit of any length may be secured.

- In United States patent of H. .Ward Leonard, No. 787 .047 granted April11, 1905. there are disclosed the advantages in the use of a braided or stranded conductor in enameledresistance units ordevices, instead of using one large wire of equivalent cross-section, by reason of the easily and better covered withthe insulatstranded or braided conductor being more ing coating than one large wire could be, and also overcomes the difliculty due to expansion and contraction when the resistance device is heated and cooled. In this way devices of this type having a low resistance have been made and used with excellent results.

In some cases, however, is is desirable to produce resistance devices having a very low resistance and even with a braided conductor, the best results cannot be obtained if the individual strands are made of too large a size. In some forms of resistance devices, a braided conductor made up of thirteen strands of No. 25 Brown and Sharpe gauge, good results can be obtained; but even with this character of conductor of, say German silver wire, the resistance is not sufiiciently low to give the results sometimes desired. If it be attempted to attain sufiicientlv low resistance ,by shortening. the conductor and applying this shortenedconductor to a support, the length will not be sufiicient to properly distribute 'or dissipate the heat. or example,. if in aresistance unit of tubular form, a braided conductor having the size of the strands as large as can be properly enameled on the tube, be shortened in order to obtain suf ficiently low resistance, it would have such a few number of turns around the tube in some instances that the heat would not be sufiiciently dissipated, because only a part of the surface of the tube would be utilized in the dissipation of heat. This would result' in the danger of burning the heavy braided conductor through the insulating coating and burn out orotherwise render the unit useless, due to excessive generation of heat at restricted areas.

By my invention I overcome the above difliculties and can produce a stranded or braided resistive conductor having any desired resistance per unit of length and still keep the size ofthe strands, in low resistance devices, small enough to permit practical and eflicient covering and protection of the conductor by an insulating coating such as vitreous enamel.

In accordance with my invention I utilize the stranded conductor, but I form the conductor of strands composed of resistive material and also strands of comparatively good conductive -material and by varymg the sizes of the strands used of the different materials and also varying the relative number of strands of the different materials, I can produce a conductor having practically any desired resistance per foot; and I thus can obtain a much lower resistance per footthan can be obtained by any of the resistance alloys used alone. I am thus enabled to secure suflicient length of the 'conductor to properly distribute the dissipation of the heat over a sailiciently large area to avoid damage to theconductor or to the resistance device from over-heating.

' For example German silver strands forming the resistive conductor may have combined therewith strands of copper, which will give a combined conductor of sufiicientbraided conductorsufliciently small to conductor and one form of resistance device and 4;.

embodying my invention.

Fig. 1 is a longitudinal section thereof. Fig. 2 is a side view showing the device before the insulating coating is applied. Fig. 3 is an enlarged section of one form of the conductor, and Fig. 4 is a detail viewshowing the end connections.

The particular device here illustrated is composed of a tube 10 of porcelain, earthenware, or other suitable material and has wound thereon the composite resistive conductor 11. This conductor 11 in this particular form is a braided conductor com posed of strands of German silver and of copper. In the enlarged section shown in Fig. 3, the 7 strands of the larger size 11" are of resistive material such as German silver and there are shown 6 strands 11 of smaller size and of low resistance material, such as copper. The tube 10 is grooved at the ends to receive the terminal connection which is formed as shown in Fig. 4. The lead wire 12 is indicated as a stranded conductor, preferably of copper, and is connected with'the conductor 11 as shown in this instance by a thin sheet of copper 13,

which is wrappedor twisted around the two conductors 11 and 12 to join them together at the end of the tube as shown in Figs. 2 The free ends of the conductors 11 and 12 are twisted together as shown at 14 so as to clamp the end connection tightly in the groove at the end. of the tube. The tube and conductor 11 and end connections .are next covered with the insulating material 15 and fired so as to form an adhesive insulating and protective coating, preferably of vitreous enamel.

The composite conductor is preferably made of strands braided together, but they may be twisted together andin some cases may lie parallel to each other and the composite conductor may be flat or round or otherwise, according 'to the requirements of the particular case.

Although I have illustrated 'an embodiment of my invention as applied to atube,

the invention is also applicable to devices having flat surfaces and to various types and forms of resistance devices. My improved conductor is also advantageous in some cases where it: is not supported throughout its length, and in some cases it may not be covered by an insulating coating.

In the following claims it should be understood that the reference to the composite conductor as being one formed of strands, means a conductor in which the strands are continuous throughout the length of the composite conductor and form a unitary conductor in the construction and use of the port,'and a composite braided resistive con.-

ductor having strands of material having different specific resistances.

4. A resistance device comprising a support, and a composite braided-resistive conductor 'havin strands of material having different specific resistances, and an insulat ing protective coating on said conductor and support.

5. A resistance devicecomprising a support, and a composite resistiveconductor having strands of material having different specific resistances, and the strands of one material being of difierent size from the strands of the other material.

- 6. A resistancedevice comprising a support, and a composite resistive conductor having strands of mater al having different specific resistances, and the, strands of one material being of difierent size from the strands of the other material, and. an insulating protective coating 0118211111 conductor and support.

7. A resistance device comprising a support, and a composite resistive conductor having strands of resistive. material and of conductive material. I

7 8. A resistance device comprising a support, a composite resistive conductor having strands ofresistive material and of conductive material, and the strands of resistive 'material being of different size from the.

strands of conductive materials 9. A resistance device comprising a support, and a composite resistive conductor having strands ofresistive material and of copper.

10. A resistance device comprising a support, and a composite resistive conductor having strands of resistive material and of copper, and an insulating protective coating on said conductor and support.

ALFRED ERNEST WALLER. 

